Solvent tolerant marine bacterium Bacillus aquimaris secreting organic solvent stable alkaline cellulase

The organic solvent tolerant bacteria with their physiological abilities to decontaminate the organic pollutants have potentials to secrete extracellular enzymes of commercial importance. Of the 19 marine bacterial isolates examined for their solvent tolerance at 10 vol.% concentration, one had the significant tolerance and showed a relative growth yield of 86% for acetone, 71% for methanol, 52% for benzene, 35% for heptane, 24% for toluene and 19% for ethylacetate. The phylogenetic analysis of this strain using 16S rDNA sequence revealed 99% homology with Bacillus aquimaris. The cellulase enzyme secreted by this strain under normal conditions showed an optimum activity at pH 11 and 45 degrees C. The enzyme did show functional stability even at higher pH (12) and temperature (75 degrees C) with residual activity of 85% and 95% respectively. The enzyme activity in the presence of different additives were in the following order: Co+2 > Fe+2 > NaOCl2 > CuSO4 > KCl> NaCl. The enzyme stability in the presence of solvents at 20 vol.% concentration was highest in benzene with 122% followed by methanol (85%), acetone (75%), toluene (73%) and heptane (42%). The pre-incubation of enzyme in ionic liquids such as 1-ethyl-3-methylimidazolium methanesulfonate and 1-ethyl-3-methylimidazolium bromide increased its activity to 150% and 155% respectively. The change in fatty acid profile with different solvents further elucidated the physiological adaptations of the strain to tolerate such extreme conditions. (C) 2011 Elsevier Ltd. All rights reserved.